Prime Minister Junichiro Koizumi on Tuesday convened a special meeting of his cabinet in the afternoon to approve the controversial plan - which critics say is ill-conceived and violates Japan's pacifist constitution - after talks with the head of his government coalition partner, the New Komeito Party.
"The cabinet approved a basic plan. The meeting only lasted five minutes," a spokesman for the prime minister's office said, without providing further details.
Koizumi is expected to hold a news conference to explain his decision which comes as surveys show that most of the public opposes sending troops at this time, and follows the killing of two Japanese diplomats in Iraq late last month.
No member of Japan's military has fired a shot in combat or been killed in an overseas mission since World War Two, although they have taken part in United Nations' peacekeeping operations since a 1992 law made that possible.
The plan will allow troops to be sent during a one-year period starting 15 December, but will not set a specific date for the dispatch or the size of the mission, media said. The bulk of the forces are expected to go next year.
Tokyo intends to eventually send 500 to 700 soldiers and equip them with the heaviest artillery they have ever taken
overseas, according to media reports.
The army will have portable anti-tank rocket launchers and recoilless guns to protect against possible human bomb attacks, the reports said.
Seven or eight planes from the air force as well as three transport vessels and three destroyers from the navy are also
expected to be sent to Iraq, the reports said.
Japan's constitution renounces the right to go to war and
prohibits the nation from having a military, but has been
interpreted as allowing Japan to have forces for self-defence.
Recent governments have stretched the constitutional
constraints and debate over revising the pacifist clause is
heating up. Koizumi is in favour of making such changes.
A law allowing troops to be sent to help rebuild Iraq was enacted in July, but specifies that military staff be sent only to "non-combat" zones.
A civic group member protests
Japan's controversial decision
The killing of the two diplomats near Saddam Hussein's home town of Tikrit and growing attacks against non-US personnel in Iraq have raised fears that Japanese troops may become targets if they are sent there.
Many Japanese also fear they could become the targets of
attacks at home, following reported threats by al-Qaida to "strike at the heart of Tokyo" if Japan sends troops to Iraq.
More than 100 demonstrators protested outside the prime
minister's residence on Tuesday, shouting and holding banners
saying "No to the Iraq troop deployment".
A weekend survey by public broadcaster NHK showed that only 17% of voters favoured sending military troops to Iraq soon, 53% would support a dispatch after peace and order were restored, and 28% opposed it in any circumstance.